KINETICS AND PHYSICAL CHANGES DURING PYROLYSIS OF BITUMINOUS COALS

The pyrolysis of bituminous coals and associated physical changes have been studied. One representative sample of each bituminous subrank of low, medium and high volatile matter content was considered. Granular samples with sizes ranging from 35 U.S. mesh (500 (mu)m) to 200 U.S. mesh (74 (mu)m) were pyrolyzed both isothermally and at constant rates of heating varying from 1 to 100(DEGREES)C/min over temperatures ranging up to 600(DEGREES)C. Thermal decomposition kinetics were studied by monitoring sample weight loss as a function of time and/or temperature. Both the physical expansion and changing pore structure were followed through the pyrolysis process with dilatometry, mercury intrusion porosimetry and scanning electron microscopy. In order to study the mechanism of expansion inhibition by inorganic salts, compounds of Ca, K, Mg, Na, NH(,4)(\u27+), Sn and Zn were tested. Impregnated coal samples were analyzed for inorganic content by atomic absorption spectroscopy. Interpretation of coal pyrolysis under constant rate of heating was provided in the form of successive first order isothermal decomposition steps. Mechanistic interpretations were provided of the swelling behavior, macropore structure development, and inorganic expansion inhibition